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PO
 

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    <p>I would use queues and daemon worker threads that are always running and wait for something to arrive in the queue. This way it is guaranteed, that only one worker is working on a request. If you only want one thread to run, turn POOLSIZE down to 1, or use newSingleThreadExecutor. </p> <p>I do not quite understand your second requirement: do you mean only 1 thread is allowed to run as background task? If so, you could create another SingleThreadExecutor and use that for the background task. Then it would not make too much sense to have POOLSIZE>1, unless the work done in the background thread is very short compared to that done in the worker itself.</p> <pre><code>private static interface Request {}; private final int POOLSIZE = 10; private final int QUEUESIZE = 1000; BlockingQueue&lt;Request&gt; e = new LinkedBlockingQueue&lt;Request&gt;(QUEUESIZE); public void startWorkers() { ExecutorService threadPool = Executors.newFixedThreadPool(POOLSIZE); for(int i=0; i&lt;POOLSIZE; i++) { threadPool.execute(new Runnable() { @Override public void run() { try { final Request request = e.take(); doStuffWithRequest(request); } catch (InterruptedException e) { // LOG // Shutdown worker thread. } } }); } } public void handleRequest(Request request) { if(!e.offer(request)) { //Cancel request, queue is full; } } </code></pre> <p>At startup-time, startworkers starts the workers (surprise!). handleRequest handles requests coming from a webservice, servlet or whatever.</p> <p>Of course you need to adapt "Request" and "doStuffWithRequest" to your need, and add some additional logic for shutdown etc.</p>
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    1. POPattern for executing concurrent tasks just once
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    1. USRon
    1. USRon
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    1. COI understood that problem is that several requests with same ID can arrive, and only one should be processed.
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      1. USSergey Aslanov
    2. COI understand "I don't want to execute the same request multiple times." as to not process the same request multiple times and a queue is a perfect match here. I do not see any constraint on how many requests should be processed concurrently. BTW: Different oppinion is not worth a downvote.
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      1. USRon
    3. COVoted up to compensate the downvote. Thanks a lot for the input! :)
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      1. USmkuff
 

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